Abstract—Organic Rankine Cycle (ORC) has attracted much attention as a promising technology for an efficient conversion of low-grade energy into electricity. In this study the thermodynamic performance of transcritical ORC with varying source temperature is investigated. The system uses R134a as working fluid and its performance such as the ratio of mass flow rate, specific net work, and thermal and exergy efficiencies are parametrically investigated. Results for the source temperature ranging 160-300oC and the reduced turbine inlet pressure (TIP) up to 3 show that the ratio of mass flow rate increases with TIP for fixed source temperature. It is also shown that the specific net work, and thermal and exergy efficiencies increase with TIP in the subcritical region and have a peak in the supercritical region for each source temperature. Thermal efficiency can be raised by adopting supercritical cycle with sufficiently high source temperature.